The arrangement of myosin and accessory proteins such as C-Protein in the vertebrate striated muscle thick filament is incompletely known. Recent experiments on the structure of frog thick filaments, however, have demonstrated that the structure of vertebrate thick filaments may be amenable to analysis by a combination of electron microscopy, optical diffraction analysis, and computer image reconstruction techniques. The specific aim of the proposed research is to expand these studies of the frog thick filaments and to extend the studies to the determination and comparison of the structure of thick filaments isolated from fish, avian, and mammalian striated muscle. The major objective of these studies will be the determination of the arrangement and number of myosins per crossbridge level in these filaments and how C-protein is arranged relative to the underlying myosin. The studies to accomplish these aims will include: 1) the development of procedures fro the isolation of native thick filaments with minimal structural alteration from each of the species; 2) the use of combination of electron microscopy and optical diffraction analysis of the micrographs to assess the filament preservation; and 3) the use of computer image analysis of the filament images in the best electron micrographs to determine the rotational symmetry and arrangement of the myosin heads, and the arrangement of C-protein. These studies will provide basic scientific information about the structure of muscle, and will thus provide a better foundation for understanding how pathologic condition may affect the functioning of this tissue.